coop: (1) do not rest on the barrel. It changes a lot of things. (2) Maintain a consistent grip and trigger pull and you will hit consistently. Whenever you change anything, grip, support, trigger pull, etc., it will change where you hit. If your supports pattern changes you will hit differently as the recoil will move the barrel before the bullet has even travelled downrange. We found that out in silhouette shooting - if you change how you rest the handgun your poi will change and the further the distance the greater the change.
Your hands should either be free of contact with supports (as in the field) or fully supported. Your revolver should be rested on the frame forward of the cylinder. Your barrel should be free of contact with your rest. It is good that you are practicing simulated shooting but remember that when you are in the field you will not have the sturdy support of the bench to assist you - all you're gonna have is a couple of wobbly sticks. You might be better off practicing with your shooting sticks to see what distance you can actually hit accurately at and go from there. If you can't plant them accurately at 75 m, back down to 50. If your poi and groups change so much at 75m from 50m, possibly you should consider 50m as the farthest distance.
When shooting 'free-hand' with a 2 handed hold your groups you might hit a bit higher or your groups may open up somewhat because you are using any supports but hey, 8" at 100 yds with just a 2 handed hold isn't bad but if you are going into the field with that piece you may wish to practice more at the standing unsupported position to hit more consistently.
The difference for me is between 50 and 200m. I can knock down the 200 yd metallic silhouette (Ram) all day long (from a rest), but unless I have a perfectly clear sight picture, the furthest I will shoot with a revolver (open sights) is 50-60m. HTH. Mikey.